Sugar production apparatus

ABSTRACT

An evaporator in the form of a vacuum pan has partitions (38) providing a plurality of compartments (42, 46) between an inlet and outlet. The compartments increase in volume from the inlet to the outlet, each compartment having at least one pair of hollow fins (50). A pair of shafts (32) pass through the partitions (38) to provide vanes (58) in each compartment. The vanes (58) pass over the surfaces of the respective fins (50) to agitate fluid in the vacuum pan, the fluid passing from compartment to compartment by way of weirs. The number of fins (50) in each compartment increases from the inlet to the outlet, and the fins (50) may be heated, as may be the vanes (58). The apparatus is advantageous in preparing crystalline sugar from sugar solution, providing for even dispersal of sugar crystals and keeping the massecuite in motion before the latter in its most concentrated state leaves the compartment (46) for further processing.

This application is a PCT application. This application claims thepriority date of Jul. 28, 1989 for Great Britain Patent No. 8917313.2.

This invention concerns improvements in or relating to sugar productionapparatus and particularly to evaporators where crystalline sugar isprepared from sugar solution.

Various apparatus have been proposed in the past, for example thatdisclosed in U.K. Patent No. 1190243. Past evaporators have either beenbatch evaporators in which sugar is processed in successive batches oralternatively continuous evaporators where production is continuous. Adisadvantage of all such apparatus is the formation of sugar crystals onthe evaporator walls and other components of the apparatus, such crystalformation reducing the efficiency of the apparatus.

It is an object of the present invention to provide a continuousevaporator in which the disadvantages of prior evaporators are obviatedor mitigated.

According to the present invention there is provided an evaporatorincluding a shell, at least part of which is partitioned, between aninlet and an outlet, into a plurality of transversely extendingcompartments by spaced partitions over which, in use, fluid may flowfrom each compartment to the adjacent downstream compartment, at leastone heating fin extending transversely into each compartment, and atleast one rotatable, longitudinally extending shaft extending throughthe shell and being provided with vanes which pass over the surface ofthe respective fins to agitate the fluid to be evaporated within thecompartments.

Preferably a pair of the rotatable shafts are provided in a parallelrelation, the vanes on one shaft being staggered with respect to thevanes on the other shaft so that they inter-mesh.

Preferably also, in a direction from inlet to outlet, the number of finsin each of the compartments increases. The fins may be steam heated, andat least one pair of the fins may be arranged in each compartment toextend towards each other from respective sides of the shell.

Outer walls of the shell in the region of each compartment may be steamheated, and also the or each shaft may be steam heated. Further, thevanes may be steam heated.

Preferably each partition is provided with a weir in an edge to controlfluid passing thereover.

Preferably also the or each fin is supported on the shell such thatthere is a gap defined between the fin and the shell.

Means may be provided for maintaining the shell at sub-atmosphericpressure, and means may be provided for introducing make-up fluid intothe compartments, the fluid introduction means comprising, for example,nozzles located above the compartments. The nozzles may deliver acurtain of make-up fluid or a spray. The shell may also be provided withvapour extraction means.

Further according to the present invention there is provided anevaporator including a shell, at least part of which is partitioned,between an inlet and an outlet, into a plurality of transverselyextending compartments by spaced partitions over which, in use, fluidmay flow from each compartment to the adjacent downstream compartment,heating means for heating the fluid, and fluid make-up means locatedabove the compartments for introducing make-up fluid into theevaporator.

The fluid make up means may be nozzles adapted to deliver fluid as acurtain or a spray. Agitation means may be provided in each compartment,and heat transfer fins may be provided in each compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way ofexample only with reference to the accompanying drawings in which:

FIG. 1 is a transverse elevation through an evaporator and;

FIG. 2 is a longitudinal elevation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An evaporator in the form of a vacuum pan comprises a shell 10 having anarcuate top 12 incorporating sight glasses 14, illumination means 16 anda hatch 18 on a manway 20, none of which form part of the presentinvention and will not be described in detail. The top 12 is connectedto a base 24 by straight sided walls 22, the base comprising a centreflat portion 26 and two upwardly arcuate walls 28. The latter are eachprovided with a spaced, external wall 30 whereby heating steam may besupplied to the spacings between the walls 28, 30, to provide a heatingjacket.

Two hollow rotatable shafts 32 extend through the evaporator from an endwall 34 to an opposed end wall 36 in a parallel relation. Each shaftpasses through a plurality of spaced partitions 38 which extend from thebase of the evaporator to a point just above the half-way mark and areeach provided at one side of an upper edge with a weir 40 so that sugarand water solution, or massecuite, may flow from an inlet compartment 42defined between the end wall 36 and the first partition 38, to aneighbouring compartment 44 and so on to the end compartment 46, sevencompartments in all being provided, the compartments increasing involume from inlet to outlet.

Each compartment includes at least one pair of hollow fins 50 each ofthe fins being supported from a respective one of the arcuate walls 28and the base 26 but spaced therefrom by a gap 56. The fins 50 are hollowsuch that heating steam can pass therethrough from an inlet manifold 52to an outlet manifold 54. The number of fins 50 increases from the inletcompartment 42 which has one pair, to the outlet compartment 46 whichhas eight pairs. Each shaft 32 has a plurality of vanes 58 radiallyextending therefrom. The vanes are arranged in spaced apart sets of six,and each set, on rotation of the respective shaft, sweeps the spacebetween adjacent fins 50 or adjacent fins and partitions. The vanes 58on one shaft are staggered with respect to those on the other shaft sothat they "intermesh" to ensure good agitation of the massecuite in eachcompartment.

A vapour extraction arrangement 60 is provided in the roof 12 of theevaporator adjacent the outlet end wall 34, and supported from the roof12 there are provided a plurality of syrup introduction nozzles 62 forsupplying a curtain of syrup into the compartments. The nozzles 64 abovethe outlet compartment 46 supply sprays of syrup. Also suspended fromthe roof 12 are a plurality of sprays 66 for spraying syrup onto thesurface of the massecuite, the partitions, and the evaporator walls towash any crystals forming on the walls into the massecuite.

In operation, massecuite with seed crystals therein fills eachcompartment and steam is supplied to the fins 50 and to the externalheating jacket. Water evaporates from the massecuite thereby increasingthe degree of super saturation and causing more sugar to deposit ontothe surface of the crystals present. The agitating action of the vanes58 in each compartment causes an even dispersal of the sugar crystalsand controls their size. As the vanes 58 pass close to the fins 50 theyensure that the massecuite in contact with the fins and partitions isalways in motion, thus reducing the tendancy for crystals to form on thefins or settle out of the massecuite. Similarly the tips of the vanessweep close to the arcuate walls 24 and reduce the tendancy for crystalsto form on these walls. It is known that crystals tend to form at sharpangles and consequently the gap 56 between the fins and the arcuatewalls 28 is provided to encourage circulation along the length of thewall 28 thereby reducing crystal formation at this point. Theintroduction of make-up syrup through the nozzles 62 increases thevolume of massecuite in each compartment and concentrated massecuiteflows over the respective weir 40 into the adjacent downstreamcompartment where further evaporation takes place, the more concentratedmassecuite then passing to the next compartment, and being in its mostconcentrated state in the end compartment 46 from which it leaves theapparatus for further processing. The water vapour separated from themassecuite is exhausted from the sub-atmospheric shell 10 by theextractor assembly 60.

Various modifications can be made without departing from the scope ofthe invention. For example heating steam can be fed to the hollow shafts32 to increase the evaporation effect within the massecuite and to heatthe vanes 58 to reduce the formation of crystals thereon. The vanesthemselves may have steam passages therethrough and may have an ovalcross-section. The vanes of each set may be arranged in the same planeor may be in a spiral arrangement to further enhance agitation.

The number of compartments can be varied and different means can beprovided for making up the massecuite in each compartment. For examplethe nozzles 62 can be replaced by feed means in the base of eachcompartment. The base of the shell may be curved instead of flat overthe portion 26.

I claim:
 1. An evaporator including a shell having an inlet and anoutlet, at least one heating fin extending into the shell, and at leastone rotatable shaft extending through the shell, characterised in that,at least part of the shell (10) is partitioned between the inlet and theoutlet into a plurality of transversely extending compartments (42-46)by spaced partitions (38) over which, in use, fluid may flow from eachcompartment to the adjacent downstream compartment, at least one heatingfin (50) extending transversely into each compartment, each fin (50)being supported on the shell (10) such that there is a gap definedbetween the fin (50) and the shell (10), and the rotatable,longitudinally extending shaft (32) being provided with vanes (58) whichpass over the surface of the respective fins (50) to agitate the fluidto be evaporated within the compartments (42-46), including the fluid atthe surfaces of the fins (50) and the fluid in the gaps between the fins(50) and the shell (10).
 2. An evaporator according to claim 1,characterised in that a pair of the rotatable shafts (32) are providedin a parallel relation, the vanes (58) on one shaft being staggered withrespect to the vanes (58) on the other shaft so that they inter-mesh. 3.An evaporator according to claim 1, characterised in that the shaft (32)is steam heated.
 4. An evaporator according to claim 2, characterised inthat each shaft (32) is steam heated.
 5. An evaporator according toclaim 1 or 2, characterised in that in a direction from inlet to outlet,the number of fins (50) in each of the compartments increases.
 6. Anevaporator according to claim 1 or 2, characterised in that at least onepair of the fins (50) is provided in each compartment (42-46) to extendtowards each other from respective sides of the shell (10).
 7. Anevaporator according to claim 1 or 2, characterised in that the outerwalls of the shell (10) in the region of each compartment are steamheated.
 8. An evaporator according to claim 1 or 2, characterised inthat the vanes (58) are steam heated.
 9. An evaporator according toclaim 1 or 2, characterised in that each partition (38) is provided witha weir (40) in an edge to control fluid passing thereover.
 10. Anevaporator according to claim 1 or 2, characterised in that nozzles (62)are located above the compartments, (42-46) for introducing make-upfluid into the compartments.
 11. An evaporator according to claim 10,characterised in that the nozzles (62) are adapted to deliver a curtainof make-up fluid.
 12. An evaporator according to claim 10, characterisedin that the nozzles (62) are adapted to deliver a spray.